Armature deformation behaviour with shape keys
I got this working by using the "Corrective Shape Key" addon. So I posed the armature in the end position I wanted. Then I selected the mesh object (bulb) and hit the "create duplicate for editing" in the Shape Keys group of the objects data tab.
Selecting both (copied first and then original) objects and hitting "Join as Shapes" from the same menu creates a new shape key with the copied objects shape as final mesh deformation of this shape key.

I then did this with all four directions the bulb is able to bend.
This work nicely with one nasty exception. The motion is not exactly a copy of the armatures motion, the top of the bulb changes length during bending, which in the armature is forbidden. The bulb is actually attached with top and bottom lips to metal parts. So now when I make the angle sweep, a gap between the bulbs lips and the upper metal part opens and closes again. I hope to get around this issue soon...